Fig. 3.

Group mean behavioral influences upon circulating leptin. The abscissa represents time before, during, and after the constant routine. To account for differences among subjects, the ordinate is expressed in normalized units as the percentage of the individual’s maximal leptin across the protocol. All data collected in the first 5 h of the constant routine were excluded from analysis to avoid the effects of altered posture and sleep-wake transition. Any circadian rhythmicity in the individual data were subtracted before group analysis. The mean and SE values of the data are shown. There was a significant decrease in leptin across each sleep period (when subjects also were fasting), and there was a significant increase in leptin during prolonged wakefulness (when subjects were receiving identical small snacks every 2 h).